Allow disabling automatic reorientation in `ImageDecoder`

In PDFs, there are frequently images that do have orientation information in the metadata, but they must not be taken into account during rendering.

https://github.com/mozilla/pdf.js is used all over the web and in some browsers, and takes advantage of ImageDecoder when available, leading to ridiculous performance improvement. They would like to not reorient images, or more accurately, not have to have them reoriented twice (once by the browser engine, and once themselves).

Quoting the PDF spec (https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/PDF32000_2008.pdf#page=43, bottom of the table):

Parameters that control the decoding process as well as other metadata is embedded within the encoded data
stream using a notation referred to as “markers”. When it defined the use of JPEG images within PostScript data
streams, Adobe System Incorporated defined a particular set of rules pertaining to which markers are to be
recognized, which are to be ignored and which are considered errors. A specific Adobe-defined marker was also
introduced. The exact rules for producing and consuming DCT encoded data within PostScript are provide in
Adobe Technical Note #5116 (reference). PDF DCT Encoding shall exactly follow those rules established by
Adobe for PostScript.

The reference is https://pdfa.org/norm-refs/5116.DCT_Filter.pdf. There is no mention of orientation, and so it has to be ignored for compliance.

I simply propose the following addition to the spec:

partial dict  ImageDecodeOptions {
    boolean ignoreOrientationMetadata = false;
}

The issue identifies ImageDecoder and the ImageDecodeOptions WebIDL definition as the entry point; start by reviewing that proposal and the linked PDF and DCT references. Done means reaching a settled specification for disabling orientation metadata handling without requiring a second reorientation.